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V O I C E

R E S E A R C H

,

ngo Titze

FREQUENCY IM E

Phon at ion Threshold Pressure

pressure

e-

quired to initiate

ngo lit:e, Ph. 1 .

and

ustain

ssociate Editor

phonation. On purely theoretical

ground (Titze, 1988), the threshold

pressure is lowered by reducing vis-

cous energy losses in vocal fold tis-

sue, by lowering the mucosal wave

velocity, or by reducing the pre-

phonatory glottal width. The thresh-

old pressure is also lowered by in-

creasing the vocal fold thickness.

Threshold pressures range between

0.1 and 1.0 kPa (approximately 1-10

cm H2O .

The theoretical treatment cited

above did not include the effect of

fundamental frequency (F,) on any

of the variables, although it is sus-

pected that mucosal wave velocity

increases with F, and vocal fold

thickness is known to decrease with

F,, (l-lollien & Curtis, 1960). Both of

these changes would raise P. with

increasing F,. An experimental study

by Finkelhor et al. (1987) showed

that this was indeed the case. Al-

though this study was primarily in-

tended to show the effect of tissue

hydration on

P,,

the frequency ef-

fect was quite evident. A composite

graph for the four larynges is shown

as the curve labeled F in Figure 1.

Note the dramatic rise in P,, with

increasing F,,.

Two other experimental studies,

and perhaps the most direct ones

pertaining to P,, were conducted by

Gramming (1988) and Verdolini-

Marston et al. (1990) on human sub-

jects. The Verdolini-Marston et al.

study related closely to the

Finkeihor et al, study in that hydra-

tion effects were included. Three

males and three females produced

barely audible sounds at three

pitches (low, medium, and high) and

three conditions of hydration (nor-

mal, dry, and wet; the hydration was

induced by environmental humidity,

medication, and ingested water).

The threshold pressure was mea-

sured indirectly by the technique de-

scribed by Smitheran and Hixon

(1981) for mean subglottal (lung)

pressure.

c h

again increased system-

atically with F,,, as shown in Figure 1

5,

4

5

0.

-

0

4

I

05

5

0

0

.0

0

0

0

0

0

0

00

Range of F

n

Figure I. Change of phonation threshold

pressure with fundamental frequency

F0.

Data set( is from Cram ming (1988), F is

from Finkeihor et al. 1988), V is from

Verdoljnj-M arston et al. (1990), and C is from

Cleveland and Sundberg (1985). One kPa

(kilo Pascal) is a pressure of approx imately

t e n c m 1 1 2 0 .

by the curves labeled V (solid line

for males and dotted line for fe-

males) for the normal hydration

case. (For dry and wet conditions,

the same general pattern of P,

as a

function of F,, was observed, but the

threshold shifted up for the dry and

down for the wet condition.) In the

Gramming (1988) study, hydration

was not altered, but the subject pool

was larger (10 normal males and 10

normal females). Results are shown

by the curves labeled G in Figure 1

One other study by Cleveland and

Sundberg

1985)

is noteworthy. In

this study, phonation threshold pres-

sure was not targeted directly, but

soft phonation was contrasted

with medium and loud phona-

tion for a variety of pitches. Results

are also plotted in Figure 1 (curve

labeled Q. The subjects were three

male singers, a baritone, a bass, and

a tenor. The probable reason that

lung pressure is so much greater for

these singers than for the nonsingers

is that they rejected pure falsetto as a

legitimate mode of phonation. They

probably phonated in a mixed regis-

ter and did not target the threshold

of phonation. At low pitches, how-

ever, the pressure values merge with

those of other data sets. In all of the

studies, low frequency pressures

cluster around 0.3 to 0.4 kPa (about

3-4 cm H2O .

What we learn from these studies

is that there are natural laws that re-

quire a singer to raise lung pressure

at higher pitches, just to get the

voice going. The more we can do to

lower this threshold pressure (by

good technique, hygiene, or other-

wise), the less effortful our phona-

tion will be. What is yet to be under-

stood is the control we have over the

various factors that influence

phonation threshold pressure.

R EF ER EN C ES

Cleveland, T., & J. Sundberg. (1988). Acous-

tic Analysis of Three Male Voices of Differ-

ent Quality. In A. Askenfelt. S. Felicetti,

E. Jansoon, & J. Sundberg (Eds.),

SMAC

83, Proceedings of the Stockholm Music

Acoustics Conference pp.

143-156). Stock-

holni: Royal Swedish Acad. of M usic.

Finkelhor BK. I. Titze.

P. Durham.

(1987). The E ffect of Viscosity Changes in

the Vocal Folds on the Range of Oscilla-

t ion. J. of Voice, 1 4),

3 2 0 - 3 2 5 .

Cramming, P. (1988).

The Phonetogram. An

Experimental and clinical Study.

Depart-

ment of O tolaryngology, Universi ty of

Lund, M almO, Sweden.

Hollien, H., & J. Curtis. (1960 ). A Lam ina-

graphic Study of Vocal Pitch.

J.Speech

Hear. Res., 3 4),

3 6 1 - 3 7 1 .

Smitheran, J., & T. Hixon. (1981). A Clini-

cal Method for Estimating Laryngeal Air-

way Resistance During Vowel Phonation.

J. Speech H ear. Dis., 46,

1 3 8 - 1 4 6 .

T itze, I . (1988). T he Physics of Sm all-

Amplitude Oscillation of the Vocal Folds.

J. Acoust. Soc. Am., 83 4), 1536-1552.

Verdolini-M arston, K., 1. Titze, & D. Druker.

(1990). Changes in Phonation Threshold

Pressure with Induced Conditions of Hy-

dration. J,

of Voice, 4 2),

1 4 2 - 1 5 1 .

A

odest

amount of data

has recently

been published

on phonation

threshold pres-

sure P,), the

minimum lunt

MARCH/APRIl. 1991

HE: NATS JOURNAL

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